The performance of many devices fabricated using semiconductor methods is critically dependent upon the three-dimensional (3D) structure thereof. For example, the performance of a perpendicular magnetic recording (PMR) write pole is highly dependent upon the sub-surface shape of the write pole under the air bearing surface (ABS). To obtain information about the efficacy of manufacturing methods of these and other devices, it is desirable to perform metrology on micrographs of cross sections of the write pole at various orientations. One such desired cross section micrograph is perpendicular to the leading edge near the center of the pole. This cross section allows metrology on various write pole characteristics, such as the leading edge bevel and throat height.
Typically, cross sections are obtained by milling a device near a desired cut location, and then obtaining a micrograph of the milled surface. For example, dual beam focused ion beam, scanning electron microscope (FIB/SEM) systems are often used for cross sectional metrology. Such systems can perform milling operations, generate micrographs, and deliver cross-sectional metrology information. However, proper cut placement is necessary to obtain suitable metrology information.
The conventional approach to cross-section devices in magnetic recording heads for sub-surface metrology measurements on the devices involves the following steps: First, a low/medium magnification image of the feature of interest—for example, the ABS—for positioning and alignment is obtained. Second, fiducial markers are processed for position referencing. Third, the device is ion beam milled in proximity to the fiducial markers using fixed, pre-defined milling parameters. Finally, imaging and metrology measurements are performed on the final cut face surface.
Often, especially during research and development stages, this inflexible approach provides insufficient efficiency and accuracy. For example, there may be multiple designs per wafer, per section, or per rowbar; devices may have different geometries within a wafer, a section, or a rowbar; and immature process may have intrinsic process variations. These variations often result in widely variable geometries with very tight dimensional windows for the final cut face surface placement which allow accurate metrology in the final image.